Air Breathing PEM Fuel Cells in Aviation

Aviation industry and governing bodies have set out to significantly reduce the environmental footprint of aviation. The visions brought forward request such low emissions that continuous optimization and advancement of current technology alone are not sufficient. This has led research groups to explore disruptive paths of innovation for aircraft and a trend to the electrification of onboard systems in more electric aircraft. Providing the required electric power using fuel cells and batteries not only promises the reduction of carbon emissions and noise but also allows for system level optimizations using synergy effects from a multi-functional system-integration that aircraft design could benefit from. At the same time using fuel cells in aircraft environments provides great challenges towards system design. System weight and size constraints require the use of air breathing fuel cells in commercial aircraft and airliners. This results in operation at low pressure and temperature which in term confronts the system design with two problems. First the low air density makes cooling of power systems difficult especially considering the low operating temperatures of PEM Fuel Cells. Second the low ambient temperature means the ingested air will heat up much more than during ground operation and in term will remove more water from the fuel cells, making water management and fuel cell operation strategies more important and complicated than in other applications. Also ambient conditions very rapidly change in air, adding even more complexity to the application. Taking into consideration possibilities of advanced aerodynamic concepts like distributed propulsion and propulsion/wing vortex interaction, that electric propulsion could enable, Fuel cells could be of even larger benefit for aviation when considering a larger time-frame. All-electric aircraft could potentially be emissions-free and very low noise, thus enabling sustainable, environmentally friendly aviation. While not yet feasible for large passenger aircraft, application of such systems is currently being researched in aircraft like the HY4 enroute to this goal. This presentation will discuss the challenges of fuel cell operation in-flight, as well as introduce the concepts for multifunctional fuel cell APU replacements for A320 type aircraft and drive-trains for all-electric aircraft. Finally results from ground- and flight-testing of the all-electric fuel cell powered HY4 aircraft will be discussed.